Left to right, Quincy Stivers, 7, Maddie Marchand, 7, and Aiden Stivers, 5, take a break from hiking while on a tour of the Hetch Hetchy area with their parents and a group folks interested in Restoring Hetch Hetchy.

California farmers could save enough water each year to fill Yosemite's Hetch Hetchy reservoir 16 times by using more efficient irrigation techniques, according to a study that is bound to be highly controversial among the state's powerful agriculture interests.

The report, released today by the Pacific Institute, an Oakland water policy group, also recommends that the state rethink its historic water rights system and boost water prices. Both measures, in theory, would spur agricultural users to use less water at a time when climate change, urban growth and ecological restoration are expected to further cramp water supplies.

"If we want to have a healthy agriculture economy, the only real option is to figure out how to produce more food with less water," said Peter Gleick, president of the Pacific Institute and co-author of "Sustaining California Agriculture in an Uncertain Future."

Farmers agree water supplies are stretched, but they disagree on the cause. During recent "fish vs. farm" rallies in the Central Valley, protesters decried environmental rules that have cut water exports from the Sacramento-San Joaquin River Delta to protect endangered fish species.

What's more, farmers say, they are doing their part. For instance, California growers in 2000 produced double the volume of crops in 1967 with only 2 percent more water, according to Mike Wade, executive director of the California Farm Water Coalition.

Further, sweeping changes to water prices or supplies would simply hammer an industry reeling from a three-year drought, he added.

"You can't just wave a magic wand," Wade said. "There are consequences. It affects things like ... what consumers can put their hands on at the grocery store."

But maintaining the status quo isn't an option, Gleick argues.

"California agriculture is in trouble," Gleick said. "If we continue doing the things the way we've always done them ... there's not going to be enough water - that's indisputable."

California's produce growers, cattle ranchers, and rice farmers use about 34 million acre-feet of water each year (one acre-foot equals about 326,000 gallons), compared with 8 million acre-feet used in cities, according to Gleick.

In a 2003 study, Gleick found cities could save 2.3 million acre-feet - nearly 30 percent, compared with the 16 percent prescription for agriculture (the report said farms could save 4.5 million to 6 million acre-feet a year).

Gleick's recommendations for the agriculture sector range from relatively simple to positively thorny. In addition to increasing drip rather than "flood" irrigation, Gleick proposed re-examining state water rights and renegotiating higher prices for long-term federal water contracts as ways to promote conservation.

The report also called for better monitoring of water supplies.

"There are a lot of districts that have no idea how much water they use," said David Sunding, co-director of the Berkeley Water Center. "That needs to change. We're past that point in California."